By Jacob Schor, ND, FABNO
March 06, 2017

Nutrition-focused medical practitioners have advised men with prostate cancer to take supplemental zinc for so long that few can still remember where this practice originated. Several papers now suggest zinc may actually be ill advised for these patients to take.

Zinc levels in the prostate gland are higher than in any other soft tissue of the body, so it was easy to assume that zinc is important for prostate function and health. On top of this, zinc levels in healthy prostate tissue are almost 7 times as high as in prostate cancer tissue.1 Several cell culture studies reported that the addition of supplemental zinc inhibited prostate cancer cell growth.

Iguchi reported in 1998 that addition of zinc triggers necrosis in prostate cancer cells.2 Liang reported in 1999 “that zinc inhibits human prostatic carcinoma cell growth, possibly due to induction of cell cycle arrest and apoptosis. There now exists strong evidence that the loss of a unique capability to retain high levels of zinc is an important factor in the development and progression of malignant prostate cells.”3 Zinc was reported to inhibit prostate cancer invasion.4 It was not unreasonable to think that taking zinc might have similar actions on prostate cancer in men as it does on prostate cancer cells in petri dishes. And so men started to take zinc supplements. Lots of zinc supplements.

It was only a few years until signs started to appear that this assumption might not prove true. In July 2003 a paper published in the Journal of the National Cancer Institute reported that taking up to 100 mg of zinc per day did not change risk of prostate cancer, but that men who took more than 100 mg/day had more than double the risk of advanced prostate cancer compared to men who did not take zinc. Men who took any supplemental zinc for more than 10 years also had double the risk of prostate cancer (n=46,974).5

These cautionary findings were confused by a 2011 Swedish study that assessed dietary zinc levels in 525 men when they were first diagnosed with prostate cancer. Those with high dietary zinc intake had a 36% lower risk of dying from prostate cancer than those with low intake. These results strongly suggested that "high dietary intake of zinc is associated with lower prostate cancer-specific mortality after diagnosis, particularly in men with localized disease.”6 Keep in mind this study compared zinc intake from food, not from supplements.